Motorcycle ignition are subjected to failure due to many reasons. Even those aftermarket racing cdi are vulnerable to failure. In this article, a famous well known small motorcycle ignition controller in asia got burned by a user by unspecified condition and so handed over to me for inspection internally. It has no activity whatsoever when plugged to a Yamaha Mio scooter, External view of the casing told me there is one small hole with black mark on it indicating that this cdi got a burned component inside and probably the cause is still unknown after i have not open the entire ignition controller and so let us begin the tear down for further analysis.
Same as to those CDI i opened before, need to be very careful not to damage the components inside. The cover will be wasted part of this operation. The ignition controller is heavily coated with rubber epoxy resin, but can easily be stripped off by a piece of pointed wooden material.
Carefully begin the sides first to see the edge of the board. In the photo, i stripped the area of the burnt component to see that component, with the orientation of the parts installed, i knew it has something to do with the High Voltage generator circuit. The part number is totally erased by the burned component. So i need to dig deeper.
Continuing the process of exposing the board as follows. Exposing first the bottom view of the board will make it easier to find where tall components are located and also exposed the area of damaged.
There are also damaged copper foil, indicating not only one part is defective. Sign of too many problems the cdi encountered from the user.
After removing the entire coating of the bottom view of the board, just continue the removal now of the component side with many PATIENCE at hand.
And here is the partial section of that top area of the board. It took hours of removing the stubborn rubber coating. We all know the reason of those coatings before, it protects the entire board from moisture, vibration, dirt and other nature elements that may limit the life of the CDI during operation.
Exposing the board further, Have to desolder some components due to spaces of each part, nearly break a damn 1/8th watts resistor. The silk screen has a marking of component so removing parts and writing down every value of the component is critical from here. And that's the way it should when repairing such item, for once a part gets damaged and value is no longer visible, it will be a waste of time figuring out that UNKNOWN part without any schematic diagram in hand.
Nearing to the teardown,
Let us take a closer look at the damage component. Tracing the entire board and drawing the schematic gives me that the burnt component with a silk screen suffix of S1 made me think it is a Thyristor (SCR) that switches the capacitor to discharge the energy to the ignition coil. a major part of the cdi. I suspect that the output of this cdi got shorted with the igntion coil.
With some part now desolder on the board to thoroughly clean the cdi, Component testing made it easier to find other that failed. Overall it has four components that needed to be replaced to make it working again. As of this time, I am gathering the components needed for it to run again, will do some bench testing using pulse simulator. As far as i am concern, with the look of those failed parts of this ignition controller,
There are many primary reason why it ended this way
1. Overvoltage of the supply
2. Temporary short at the ignition coil area. (output of the CDI to the ignition coil)3. Wrong wiring connection
4. The least is factory defect...(found some solder residue that may causes the short path of each component in the high voltage section of this cdi)
Part II of this repair will be compose of the bench testing and actual video of it when back to life.
